Liquid atomizers are widely used in industrial, agricultural, propulsion and other systems. Such liquid atomizers are typically used to produce a spray (i.e., a liquid/gas mixture including fine droplets of the liquid) for various purposes, such as creating a spectrum of droplets, control or metering of liquid throughput, dispersion of liquid droplets for mixing with surrounding air, and generation of droplet velocity or penetration. In one embodiment, the transformation of bulk liquids to sprays can be achieved, for example, by directing various forms of energy, such as hydraulic, pneumatic, electrical, acoustical, or mechanical energy, to the bulk liquid to cause the liquid to break up into droplets.
Pneumatic atomizers are often used in gas turbine engine applications. Most pneumatic atomizers used in gas turbine engine applications include an atomizer tip which includes two components: a fuel swirler and an air swirler. The fuel swirler may receive a liquid in one end and eject or feed the liquid through an exit orifice, typically in a spiral motion, to generate a film or spray of liquid. The air swirler (such as a discrete jet air swirler) may direct pressurized air towards the outputted liquid such that the pressurized air impinges upon the liquid, breaks the liquid into a spectrum of droplets, and disperses the droplets.
In such pneumatic atomizers, the air streams are typically either high volume, low-pressure drop air streams, or low volume, high-pressure drop air streams that are directed toward the bulk liquid to impinge upon, or shear against, the liquid film or spray. The air streams directed toward or over the bulk liquid often includes a rotational component or a “swirl” motion to enhance mixing and interaction with the liquid surface, as well as to improve dispersion of the liquid droplets. Thus, the air streams may be arranged and controlled to produce the desired distribution and uniformity of fuel droplets, as well as the desired angle of the fluid droplets spray. In particular, in gas turbine applications, the atomizer preferably provides a fuel spray that allows the gas turbine to operate over a wide range of combustion limits over extended periods of time with low acoustic noise and low emission pollutants.
Air swirlers are often still designed by trial-and-error techniques, which involves much development effort and time to fine tune the design geometry or to achieve the desired spray characteristics. Furthermore, the air streams emerging from the air swirler may overlap and cross each other in the vicinity of the air swirler, which results in energy loss, decreased spray control and narrow spray angles. When used in a gas turbine engine, such atomizers with crossing air streams may result in a relatively narrow range of combustion stability limits, excessive acoustic noise, and high levels of smoke at low power conditions. Such atomizers may also experience carbon formation on the atomizer face and difficulty in high altitude re-light. In some prior art designs, the air streams are designed to cross to collapse the spray in an attempt to reduce smoke and alleviate the presence of hot spots on the liner walls.
Accordingly, there is a need for air swirlers and atomizers which are more efficient and effective, as well as a methodology for designing air swirlers and atomizers.